Robotised workstation for quality control of metal castings

Abstract

The present invention provides a robotised workstation for testing the quality of metal castings, comprising an arm robot (1) with an effector (9), a vision system (2), a loading conveyor (3), a weighing processor (4), a test conveyor (5) an automation system for controlling the arm robot (6), and a finished goods receiving station (7) and a defect receiving station (8); a workstation such that the effector (9) comprises a three-point magnetic gripper (10) and, positioned between the magnetic gripper (10) and the effector mount (12), in the effector support frame (14), a modal hammer (11) with a modal hammer striker (15) having a feed direction perpendicular to the plane determined by the support points (13abc) of the magnetic gripper (10).

Description

[0001] Robotised workstation for quality control of metal castings

[0002] The object of the present invention is a robotised workstation for quality control of metal castings by acoustic resonance method with the possibility of being used to identify, measure and select products in the production process.

[0003] There are known semi-automatic and automatic non-destructive methods for manual testing of products, the latter applied mainly for the testing of objects with a simple geometry such as pipes, sheet metal or elements of a non-variable geometry, tested in large quantities, such as railway rails, as well as objects difficult or dangerous to access for a tester carrying out manual tests. The main advantages of automatic testing are the possibility of computerised recording and subsequent processing, analysis and verification of data, the high speed of testing, the possibility of easy visualisation of the test results in the form of B, C and even 3D images, the possibility of partially or fully automatic classification of the tested element as per the acceptance conditions in a more objective manner independent of the operator. For example, there are known automatic ultrasonic testing systems comprised of an array of ultrasonic transducers, a signal acquisition and imaging system, a system providing movement and analysing the position of the transducers, and a system providing an acoustic coupling between the transducers and the test object. Depending on the application, such a system may feature additional systems, such as an independent power supply.

[0004] There is known a non-destructive testing method for metal castings intended automatic application, consisting in excitation and subsequent measurement of the natural frequency of the castings, or measurement of the vibration decay time following their excitation, i.e., the measurement of the vibration damping capacity. The obtained value of the first resonance frequency, i.e., the natural frequency or the vibration damping time of the tested casting, is compared against the natural frequency or the vibration damping time of a standard defined for a given casting, which meets all the requirements following from the technical acceptance conditions. The natural frequency of the component, i.e., the vibration falling within the audible frequency of 20-20,000 Hz, is determined by a number of factors, such as the shape factor, e.g. the geometric development of the casting body, the size and weight of the casting, the thickness of its walls, and factors dependent on the physical constants of the material from which the casting is made, e.g. the modulus of elasticity or the modulus of density, i.e. determined by its texture and structure. If the shape factors of a certain number of elements remain constant, then the natural frequency of the element can serve as an indicator of the quality of the element originating from the physical constants of the material, i.e. from e.g., the content of certain components of the structure having acoustic properties other than those of the matrix, e.g. the type and shape of graphite precipitates in cast iron, silicon precipitates in aluminium alloys, or breaks in the continuity of the element's material structure in the form of various defects, cracks, etc.

[0005] In solid media exhibiting volume and form elasticity, it is possible to propagate both longitudinal and transverse waves and waves being combinations of the same, e.g., Reyleigh waves and Lamb waves. In unconstrained model systems, only longitudinal and transverse waves propagate. In media constrained (where the wavelength is greater than the dimensions of the medium) by a single surface, surface waves propagate, whereas in media constrained by two parallel surfaces (e.g. plates, shells), Lamb waves propagate. As castings are not usually model systems (e.g. slab, cylinder), but are rather characterised by significant shape development, their natural frequency is the resultant of these waves in different proportions, following in each case from the shape of the castings. In the case of sound wave propagation in anisotropic media, such as technical alloys with discontinuities in the medium (porosity, cracks, etc.), the distribution of the acoustic field is distorted if there is an obstacle within it having dimensions commensurate with the wavelength, understood to be an enclosed area with different acoustic properties than the medium (different density, different elasticity), wave reflection, deflection and diffusion occurs on the phase surface of the obstacle, leading to a disturbance overlapping the acoustic field, which determines the natural frequency of the object. In principle, this kind of tests do no define the type of a defect (structure error, shape error, material discontinuities, etc.); however they allow to conclude that the casting does not comply with the technical conditions of acceptance.

[0006] There are known test stands for acoustic testing of industrial products, comprised of essentially a mechanical vibration excitation device, a directional microphone, a laser or other detector for collecting vibration data, a test bench for placing the test casting on it, filters and a signal amplifier, as well as a data transducer for visualising and analysing the acoustic field for comparing the natural frequency of the casting model with the natural frequency of the test casting. For example, from the Chinese utility model description CN217638860U, there is known a device for testing the quality of a connection of metal parts formed by means of bolts or rivets, comprising a striker mounted on a spring-loaded cylinder terminated by a roller for exciting vibrations, which are read and measured by means of a sensor adjacent to the tested product by means of a tip equipped with a roller connected to the measuring device. From the UK patent description GB 1516785 there is known a method and a device for testing the quality of cast iron elements, in particular ductile iron elements. The device according to that method comprises a construction to which the test product and the reference product are attached, whereby in the process of testing a batch of articles, the reference product and the test article are vibrated, the resulting vibrations are subsequently analysed and the results for the two articles are compared with each other. In these known solutions, the tested product is immobilised in a test area having a shape adapted to the type and the shape of the product prior to applying the excitation force to it by means of fixing elements adapted to the product in question, in order to prevent it from moving as a result of the force applied, which could distort the test result. Simultaneously, the place of application of the excitation force is fixed for each test item and the excitation device is permanently positioned in the test bench to achieve the fullest possible repeatability of the test conditions for each test item in a batch. In these known devices product testing is carried out in a single step, without the possibility of changing the test conditions according to the previously obtained results, at most with the possibility of repeating the test according to predefined assumptions determined by the device design.

[0007] There are known six-axis industrial robots having six axes that allow the manipulation of objects within six degrees of freedom: three translational stages, which realise the first three axes of the robot, and three rotational stages realised by a robotic cluster - usually of a spherical type. These robots enable carrying out tasks in a large workspace with considerable speed and precision, including any effector orientation.

[0008] There are known various types of effectors, such as grippers including magnetic grippers equipped with permanent magnets, electromagnets or combinations thereof. These grippers are designed in such a way as to ensure that the design is compatible with the function performed (gripping, holding, releasing objects) and, additionally, to minimise the weight in order to reduce the static and dynamic stresses on the robot, minimise the dimensions to reduce the working space required for the grippers, define the gripping force, increase the reliability and the gripping firmness.

[0009] The purpose of the present invention is an acoustic resonance quality control station for testing metal castings having different shapes and, associated therewith, different reference conditions for carrying out test, including the excitation of vibrations in the casting and the reading of the data derived from this excitation, defined according to the criteria of shape, texture and material from which the casting is made. The purpose of the present invention is also to provide a device allowing to change the test conditions of a product following obtaining certain results during a prior test by agitating the tested casting by applying a force in a different place than during the prior test. The purpose of the present invention is also a device allowing to achieve an increased testing productivity through the design of a device for exciting vibrations in a product, said design being universally applicable to castings of different shapes, with low tare weight, enabling precise force application and rapid change of test parameters.

[0010] The robotised workstation for testing the quality of metal castings according to the present invention includes a six-axis arm robot with an effector for carrying out the tasks of the workstation, a vision system for collecting image data on the shape of the casting and, based on this data, positioning the casting in the working field of the arm robot and identifying the locations of application of the vibration-inducing force based on the reference data of the casting, a loading conveyor to feed the casting into the weight processor for its further transfer to the test conveyor, a weighing processor to collect data on the weight of the casting for its inclusion as a test variable, a test conveyor with a marked working field on which the casting rests in the course of the test with a directional microphone positioned laterally to this working field and directed towards its centre to collect the acoustic spectrum. In addition, the workstation comprises an automation system for controlling the arm robot, which also includes a module for processing the test data into instructions for the robot movement, as well as a finished product receiving station and a defect receiving station, to which a casting is directed depending on the test results. The robot effector includes a three-point magnetic gripper and a modal hammer with a modal hammer striker with the direction of feed perpendicular to the plane determined by the support points of the magnetic gripper, placed between this magnetic gripper and the effector mount to the robot arm in the support frame of the effector. Such design allows the damage- sensitive striker of the modal hammer to be properly distanced and adequately covered by the magnetic gripper disc when a casting is gripped and conveyed by the effector, irrespective of the fact that the hammer striker is additionally protected against damage by a protective sleeve in a variant of the solution.

[0011] In a variant of the solution, the robotised workstation according to the present invention has a casing sleeve covering the modal hammer striker, preferably having a circular cross-section, such that the free end of the modal hammer striker is adjacent to the plane defined by the edge of the mouth of the casing sleeve. The covering sleeve protects the striker of the modal hammer in the event of an accidental slipping of the effector, during the execution of the gripping function by the effector when approaching the casting in order to grip it, as well as in cases where the casting, due to its shape, protrudes behind the face of the magnetic gripper after being gripped. The effector approaches the casting in order to apply force using the shielding function of the sleeve in two stages. In the first stage, the effector is driven onto the casting in such a way that the axis of the casing sleeve and, simultaneously, the axis of the striker is deflected relative to the adduction vector by an angle, preferably 30°, and then, after the casing sleeve comes into contact with the surface of the casting by means of the edge of the mouth of the casing sleeve, the striker is driven against the casting surface with a rotary motion relative to the point of contact until contact is made between the free end of the striker and the casting surface, after which the vibration-inducing force is applied. This design of the device allows the striker to be recessed into the casing sleeve in the rest position and to extend ahead of the plane of the sleeve mouth only in the operating position, and only when an excitation force is applied. This solution prevents damage to the striker as the effector approaches the casting, thus increasing the speed of this operation and improving the productivity and durability of the machine.

[0012] In a variant of the solution, a part of the casing sleeve at its mouth is a ring made of elastomer, preferably EPDM, to prevent damage to the striker, as well as to prevent damage and extend the life of the casing sleeve. In a preferable variant of the solution, said ring is replaceable and is fixed on the sleeve without the use of glue. In another variant of the solution, the edge of the casing sleeve mouth is coated with a 1.0- 1.2 mm thick layer of elastomer.

[0013] In a variant of the solution, the robotised workstation according to any of the variants described above has an effector support frame consisting of a U-shaped section made of a cross-sectional aluminium profile, preferably with a section of 30mm><90mm and a circumferential section made of a cross-sectional aluminium profile preferably with a section of 30mm><30mm. This variant of the solution allows to reduce the total weight of the effector, while maintaining the strength and durability of its frame due to its functions, and at the same time, through the use of cheap and widely available construction materials, reducing the cost of its manufacture and servicing. The circumferential section of the effector support frame additionally acts as a buffer to prevent damage to the modal hammer during the movement of the effector in the working field.

[0014] In a variant of the solution, the robotised workstation according to any of the variants described above has a magnetic gripper connected to the effector support frame by means of at least one vibration isolator to enable the reduction of interactions from the movement of the magnetic gripper and the modal hammer and ensure a longer service life of the device.

[0015] The robotised workstation according to the invention is shown in the embodiments in the drawing, where the individual figures show

[0016] Fig. 1 a general view of the robotic workstation

[0017] Fig. 2 an axonometric view of the effector

[0018] Fig. 3 a front view of the magnetic gripper

[0019] Fig. 4a an axonometric view of the modal hammer striker with a casing sleeve

[0020] Fig. 4b a front view of the modal hammer striker with a casing sleeve

[0021] Fig. 5 effector support frame

[0022] Fig. 6a cross section of a 30mm><90mm aluminium cross profile

[0023] Fig. 6b cross section of a 30mm><30mm aluminium cross profile

[0024] In an embodiment of the invention, the robotic workstation for quality testing of metal castings according to the invention comprises an arm robot 1 of the Nachi MC70 type with an effector 9, a vision system 2, being a 3D vision system by Keyence, whose cameras are placed on a structure prepared for this purpose, a loading conveyor 3, a weighing processor 4, being an IND570 weighing processor by Metier Toledo, a test conveyor 5, an automation system for controlling the arm robot 6, a finished goods receiving station 7 and a defect receiving station 8. The test conveyor has a marked working field on which the casting rests during the test with a directional microphone for acoustic spectrum collection placed lateral to said working field (not shown). The effector 9 comprises a three -point magnetic gripper 10 and a modal hammer 11 positioned between this magnetic gripper 10 and the effector mount 12, in the effector support frame 14, such that the modal hammer striker 15 has a feed direction perpendicular to the plane determined by the support points 13abc of the magnetic gripper 10. The modal hammer striker 15 has a casing sleeve 16 such that the free end of the modal hammer striker 15 is adjacent to the plane defined by the casing sleeve mouth edge 18. The part of the casing sleeve at its mouth comprises a bumper ring 17 made of elastomer, namely EPDM. The buffer ring 17 is separably connected to the casing sleeve 16. In another variant, the edge of the mouth of the casing sleeve 18 is coated with an elastomer layer, being 1.2 mm thick EPDM. The effector support frame 14 comprises a U-shaped section 19 made of a 30mm x 90mm aluminium cross profile A and a circumferential section 20 a made of 30mmx30mm aluminium cross profile B. The magnetic gripper 10 is connected to the effector support frame 14 by means of four vibration isolators 21. The robotised workstation is equipped with a control automation system, whose task is to supervise the production process, issue signals and control commands to the execution apparatus, receive information and signal the status of the apparatus, supervise the safety system of the robotised workstation, provide the operators with a user interface based on a SCADA system, and which includes a Simatic S7-1214FC programmable logic controller with a safety function, electrical modular and panel apparatus, Ethernet network devices, a safety apparatus, a panel computer and a Movicon 11 SCADA system. Access to the working area of the arm robot is restricted by a mobile guard protected by an electric bolt.

[0025] List of designations

[0026] 1 arm robot

[0027] 2 vision system

[0028] 3 loading conveyor

[0029] 4 weighing processor

[0030] 5 test conveyor

[0031] 6 automation system for controlling the arm robot

[0032] 7 finished goods receiving station

[0033] 8 defects receiving station

[0034] 9 effector

[0035] 10 magnetic gripper

[0036] 11 modal hammer

[0037] 12 effector mount

[0038] 13abc support points of the magnetic gripper

[0039] 14 effector support frame

[0040] 15 modal hammer striker

[0041] 16 casing sleeve

[0042] 17 ring

[0043] 18 casing sleeve mouth edge

[0044] 19 U-shaped section of the effector support frame

[0045] 20 circumferential section of the effector support frame

[0046] 21 vibration isolator

[0047] A 3 Omm x 90mm aluminium cross profile

[0048] B 30mm x 30mm aluminium cross profile

Claims

Claims1. A robotised workstation for testing the quality of metal castings comprising an arm robot (1) with an effector (9), a vision system (2), a loading conveyor (3), a weighing processor (4), a test conveyor (5) an automation system for controlling the arm robot (6) as well as a finished goods receiving station (7) and a defect receiving station (8) characterised by that the effector (9) comprises a three-point magnetic gripper (10) and, located between the magnetic gripper (10) and the effector mount (12), in the effector support frame (14), a modal hammer (11) with a modal hammer striker (15) with the feed direction perpendicular to the plane determined by the support points (13abc) of the magnetic gripper (10).

2. A robotised workstation according to claim. 1 characterised in that the striker of the modal hammer (15) has a casing sleeve (16) such that the free end of the striker of the modal hammer (15) is adjacent to a plane defined by the casing sleeve mouth edge (18).

3. A robotised workstation according to claim. 2 characterised in that the section of the casing sleeve at its mouth is a bumper ring (17) made of an elastomer, preferably EPDM.

4. A robotised workstation according to claim. 3 characterised in that the buffer ring (17) is detachably connected to the casing sleeve (16).

5. A robotised workstation according to claim. 2, characterised in that the casing sleeve mouth edge (18) is coated with a 1.0- 1.2 mm thick elastomer layer6. A robotised workstation according to any of the claims 1-5, characterised in that the effector support frame (14) comprises a U-shaped section (19) made of a 30mm x 90mm aluminium cross profile (A) and a circumferential section (20) madea 30mm x 30mm aluminium cross profile (B).

7. A robotised workstation according to any of the claims 1-6, characterised in that the magnetic gripper (10) is connected to the effector support frame (14) by at least one vibration isolator (21).

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